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## Copyright (C) 1995, 1996, 1997 Kurt Hornik
##
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2, or (at your option)
## any later version.
##
## This program is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this file. If not, write to the Free Software Foundation,
## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
## usage: chisquare_rnd (n [, r, c])
##
## chisquare_rnd (n) returns a matrix of random samples from the
## chisquare distribution with n degrees of freedom. The size of the
## matrix is the size of n.
##
## chisquare_rnd (n, r, c) returns an r by c matrix of random samples
## from the chisquare distribution with n degrees of freedom. n must be
## a scalar or of size r by c.
## Author: KH <Kurt.Hornik@ci.tuwien.ac.at>
## Description: Random deviates from the chi-square distribution
function rnd = chisquare_rnd (n, r, c)
if (nargin == 3)
if ( !(is_scalar (r) && (r > 0) && (r == round (r))) )
error ("chisquare_rnd: r must be a positive integer");
endif
if ( !(is_scalar (c) && (c > 0) && (c == round (c))) )
error ("chisquare_rnd: c must be a positive integer");
endif
[retval, n] = common_size (n, zeros (r, c));
if (retval > 0)
error (strcat("chisquare_rnd: ",
"n must be scalar or of size ",
sprintf ("%d by %d", r, c)));
endif
elseif (nargin != 1)
usage ("chisquare_rnd (n [, r, c])");
endif
[r, c] = size (n);
s = r * c;
n = reshape (n, 1, s);
rnd = zeros (1, s);
k = find (!(n > 0) | !(n < Inf) | !(n == round (n)));
if (any (k))
rnd(k) = NaN * ones (1, length (k));
endif
k = find ((n > 0) & (n < Inf) & (n == round (n)));
if (any (k))
rnd(k) = chisquare_inv (rand (1, length (k)), n(k));
endif
rnd = reshape (rnd, r, c);
endfunction
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